Ni-plated steel plate for alkali-manganese dry cell anode can and alkali-manganese dry cell anode can

ABSTRACT

The present invention provides a steel sheet material used for a positive electrode can and a positive electrode can for an alkaline manganese battery capable of improving the battery characteristics for an alkaline manganese battery, characterized in that the plated steel sheet for a positive electrode can for an alkaline manganese battery has Ni-based diffusion plating layer having on the top layer many small pinholes of diameter not greater than 1 μm, i.e. submicron pinholes, formed on the surface of the steel sheet to be used as an internal surface of the can. Said submicron pinholes preferably have, as observed by SEM, diameter in the range of 0.1˜1 μm and are present at density not less than 30 pcs/(10 μm×10 μm). The surface of the steel sheet to be used as an external surface of the can preferably has a Fe—Ni diffusion plating layer and a Ni plating layer that has been softened by recrystallization.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a national stage application of PCT Application No.PCT/JP02/00058 which was filed on Jan. 9, 2002 and published on Jul. 18,2002 as International Publication No. WO 02/055764 (the “InternationalApplication”). This application claims priority from the InternationalApplication pursuant to 35 U.S.C. § 365. The present application alsoclaims priority under 35 U.S.C. § 119 from Japanese Patent ApplicationNo. 2001-001591, filed on Jan. 9, 2001, the entire disclosure of whichis incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a plated steel sheet material used fora positive electrode can for an alkaline manganese battery and, moreparticularly, to a plated steel sheet material and a positive electrodecan for an alkaline manganese battery capable of improving the batterycharacteristics and a corrosion resistance of an alkaline manganesebattery.

BACKGROUND INFORMATION

In an alkaline manganese battery, a Ni-plated steel sheet is generallyused as the material for a container (positive electrode can) which isused for filling a positive electrode material, a negative electrodematerial, an electrolyte solution, etc., and which is also used as apositive electrode terminal. Conventionally, Ni plating has beenperformed by so-called barrel plating method in which plating isperformed after the can has been formed. This conventional method mayhave problems such as insufficient adherence of the Ni-plating layer tothe internal surface of the can, or instability in the quality of theplating layer. Accordingly, such method may be replaced by a method inwhich a pre-plated steel sheet is processed into the form of a can.However, this further method which uses a pre-plated steel sheet is alsoproblematic in that, as the Ni plating layer has high hardness and lowextensibility, the pre-plated steel sheet has poor press workability andthe plating layer tends to be separated during the processing, thusleading to deterioration in corrosion resistance. In order to resolvethis problem, another conventional method may be employed in which heattreatment is performed after the Ni plating to form a Fe—Ni diffusionlayer in the interface between the Ni plating layer and the ironsubstrate so as to improve the close adherence of the Ni plating layer,as well as to improve the extensibility of the Ni plating layer byrecrystallization and softening of Ni. The use of this method has led toa significant improvement of the press workability and corrosionresistance.

In order to attain high capacity in an alkaline manganese battery, it ispreferable to increase the content of manganese dioxide in the positivemix. However, such increase may lead to an increase in contactresistance due to the low electrical conductivity of manganese dioxideitself. As a countermeasure, a conductive film is formed on the internalsurface of the positive electrode can. With such alkaline manganesebattery, although the contact resistance is initially low, the contactresistance increases rapidly after prolonged storage at hightemperature, thus leading to a degradation of the batterycharacteristics.

Examples of improvements in the above-mentioned battery characteristics,from the side of the steel sheet material, may be found in the followingpatent publications.

For example, Japanese Patent Publication No. 05-21044 describes that, asmaterial for DI drawing and ironing, hard plating such as would producecracks in Ni plating layer during the processing is effective in causingthe surface area in contact with the positive electrode material to beincreased by the cracks produced during the processing and permittingthe battery characteristics to be thereby improved. Various examples ofhard plating are described therein such as Ni plating containing organicadditives, the aforementioned plating applied via a Fe—Ni diffusionlayer, and the like, are described.

Japanese Patent Publication No. 07-122246 and 07-300695, InternationalPatent Publication WO 95/11527, and/or the like, describe a method forensuring sufficient contact with the positive electrode material byforming a very hard alloy (such as Ni₃Sn, Ni₃Sn₂, Ni₃Sn₄, etc.) platinglayer on the top layer corresponding to the inner surface of a positiveelectrode can, and producing cracks in the plating layer during pressworking.

In addition, Japanese Patent Publication No. 08-138636 discloses amethod for increasing the surface area in contact with the positiveelectrode material, and thereby improving the battery characteristics,in which Sn and Ni are plated as dual plating layer, in this order, ontoa steel sheet and disposing the plating layer converted into an alloylayer by heat treatment so as to serve as an internal surface of thepositive electrode can. In this manner, surface cracks may be producedduring press working due to the difference of extensibility between theupper layer being composed mainly of Ni and the lower layer beingcomposed mainly of Sn.

Japanese Patent Publication No. 09-306439 describes a method in which anNi alloy plating layer having different hardnesses within the platinglayer is formed such that the plating layer to be used for the internalsurface of a can has higher hardness, for increasing the surfaceroughness of the internal surface of a can during press working so as toimprove the close adherence to the positive electrode material. As anexemplary method for varying the hardness in an alloy plating layer,varying the type or the amount of the metal to be alloyed with Ni orvarying the amount of an organic additive, is disclosed in thispublication as well.

Further, in Japanese Patent Publication Nos. 10-172521 and 10-172522, amethod is disclosed in which a Ni—Co alloy plating layer is formed, orNi—Co alloy plating is applied via a Ni plating layer. As the Ni—Coalloy is very hard, very fine cracks may be produced in the platinglayer during the press working and a very fine roughness is therebyformed so as to improve the contact with the positive electrodematerial, to thereby improve the battery performance.

Japanese Patent Publication No. 11-102671 describes a method in whichNi—Ag alloy plating or Ni—Cr alloy plating is applied via a Ni platinglayer onto the surface to be used as the internal surface of a positiveelectrode can. Since both the Ni—Ag alloy plating layer and the Ni—Cralloy plating layer are very hard, very fine cracks may be produced inthe plating layer during press working and a very fine roughness isthereby formed so as to improve the contact with the positive electrodematerial, to thereby improve the battery performance.

Additionally, in Japanese Patent Publication Nos. 11-329377 and11-329378, a method is described to utilize a Ni—Bi alloy plating layerand a Ni—In alloy plating layer, respectively, to improve the alkaliresistance of the aforementioned Ni—Sn alloy plating layer having lowalkali resistance, to thereby improve the battery performance.

The various methods in prior art as described above all aim to form avery fine roughness on the internal surface of a can during pressworking, and for such purpose, a steel sheet having a hard plating layerformed thereon is mainly used to produce fine cracks in the platinglayer during press working. However, there may be a problem associatedwith the concept of producing cracks in the plating layer during pressworking that the production of cracks in the plating layer variesdepending upon the variation of the condition of the press working, andtherefore, stable battery characteristics may not be obtained.

In order to overcome the above-described problem, another method isprovided and disclosed in International Patent Publication WO 97/44835for increasing the close adherence to the positive electrode material byapplying an electrolytic treatment in acidic solution after Ni platingand thereby roughening the surface. Japanese Patent Publication No.2000-192281 describes a method in which, after discontinuously formingNi plated layers, etching is performed in an acidic solution and,further, a Ni plating layer is formed to obtain a surface having manysmall pits formed thereon. However, these methods require equipment fortreatment in an acidic solution, and are therefore undesirable in termsof cost.

It is an object of the present invention to overcome the above-describedproblems and to provide a plated steel sheet material to be used as apositive electrode can for an alkaline manganese battery and a positiveelectrode can for an alkaline manganese battery having good batterycharacteristics.

All cited references are hereby incorporated herein by reference intheir entireties.

SUMMARY OF THE INVENTION

According to one exemplary embodiment of the present invention, a Niplated steel sheet which may be used for a positive electrode can for analkaline manganese battery. For example, a Ni-based diffusion platinglayer having pinholes, as observed by a Scanning Electron Microscope(“SEM”), of diameter in the range of 0.1˜1 μm and at density of not lessthan 30 pcs/(10 μm×10 μm) on its surface is formed on the surface of thesteel sheet to be used as an internal surface of the can. A Fe—Nidiffusion plating layer and a Ni plating layer may be formed on thesurface of the steel sheet to be used as an external surface of the can.In addition, the Ni plating layer, on the surface of said steel sheet tobe used as an external surface of the can, may be softened byrecrystallization.

In another exemplary embodiment of the present invention, a positiveelectrode can for an alkaline manganese battery may be provided. Thepositive electrode can may be composed of a steel sheet which has, onthe surface to be used as an internal surface of the can, a Ni-baseddiffusion plating layer formed with pinholes, as observed by SEM, ofdiameter in the range of 0.1˜1 μm and at density of not less than 30pcs/(10 μm×10 μm) on the surface. The positive electrode can for thebattery may be composed of a steel sheet, which has a Fe—Ni diffusionplating layer and a Ni plating layer formed on the surface, to be usedas an external surface of the can. The Ni plating layer on the surfaceto be used as an external surface of the positive electrode can for thebattery may be softened by recrystallization.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a SEM photograph (×1000) showing a surface of a Ni platedsteel sheet having a number of sub-micron sized pinholes according tothe present invention;

FIG. 2 is a SEM photograph (×5000) showing a surface of a Ni platedsteel sheet having a number of sub-micron sized pinholes according tothe present invention; and

FIG. 3 is a SEM photograph (×5000) showing a surface of a conventionalNi plated steel sheet.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT(S)

As an initial matter, constructive preferences of the surface of a steelsheet corresponding to the internal surface of a positive electrode canfor an alkaline manganese battery in accordance with an exemplaryembodiment of the present invention are described below. A Ni baseddiffusion plating layer is formed on the surface to be used as aninternal surface of the can, and it is required the surface of theplating layer have many pinholes of diameter not greater than 1 μm(hereinafter referred to as sub-micron pinholes). Examples of a ScanningElectron Microscope (“SEM”) photograph of the steel sheet surface havinga plating layer containing submicron pinholes are shown in FIGS. 1 and2. Magnifications are provided as ×1000 in FIG. 1, and ×5000 in FIG. 2.As shall be described below with references to FIGS. 1 and 2, thepinholes can be hardly discerned in magnification of ×1000 (see FIG. 1),and that many pinholes of diameter not greater than 1 μm can be observedas dark shadows at a magnification of ×5000 (see FIG. 2). Small pitsformed in accordance with the conventional method as disclosed inJapanese Patent Publication No. 2000-192281 are of larger diameter ofabout 10 μm, and may be present at density of less than about 1 pcs/(10μm×10 μm), and therefore are clearly distinct from the submicronpinholes in accordance with the present invention. As a comparison, atypical surface condition of a conventional Ni plated steel sheet for apositive electrode can which has much fewer sub-micron pinholes andwhich has inferior battery performance is shown in FIG. 3 (illustratingthe magnification of ×5000).

By providing the surface of the Ni based diffusion plating layer withmany minute pinholes of diameter not greater than 1 μm, a certain closechemical adherence may be produced between the Ni based diffusionplating layer on the internal surface of the formed positive electrodecan and a conductive coating. Such layer is applied on the internalsurface of the formed positive electrode can, thus leading to animprovement of battery characteristics. The Ni based diffusion platinglayer is also effective in ensuring adequate primary rust-preventingcapability, after being formed into the can, and corrosion resistance instrongly alkaline electrolyte solution.

A Ni based diffusion plating layer refers to a layer in which Ni basedplating such as Ni plating (e.g., bright, semi-bright, dull), Ni—Coalloy plating, Ni—Fe alloy plating is applied, followed by heattreatment to convert a part or all of the Ni based plating layer into adiffusion layer. If strain has been introduced into the plating layerduring plating process, a number of sub-micron pinholes may be formedwhen diffusion takes place in the heat treatment process. Specificmethods for introducing strain include, for example, plating applied athigh current density within the range that does not give rise to a burntdeposit, plating applied at extremely low plating efficiency (forexample, using plating bath free of boric acid), and the like. It isdesirable (in order to obtain good battery performance) that sub-micronpinholes have, as observed by SEM, diameter of 0.1˜1 μm, and are presentat density of 30 pcs/(10 μm×10 μm). Pinholes having diameter of 0.1 μmcan be distinctly recognized in an image of SEM at magnification of×5000.

Next, constructive requirements of the surface corresponding to anexternal surface of a positive electrode are described. As the influenceof an external surface of a positive electrode can may be negligiblysmall related to an improvement of the battery characteristics which isone of the objects of the present invention, the following preferencesare not particularly crucial as it concerns the battery characteristics.However, since more stringent and higher corrosion resistance istypically used for an external surface of a positive electrode can,composition of a plating layer that meets this requirement is describedbelow. It is desirable that the surface to be used as an externalsurface have a Fe—Ni diffusion plating layer with a Ni plating layer ontop thereof. This permits good corrosion resistance to be obtained forthe terminal portion of the positive electrode which is subjected toparticularly severe processing. More preferably, in view of corrosionresistance, the above-mentioned Ni plating layer is softened by therecrystallization. The above-mentioned plating layer having compositestructure may be formed, for example, by adopting a method in which anFe—Ni diffusion layer is formed in a portion of a Ni plating layer byheat treatment after Ni plating, such that Ni is left as it is in theuppermost layer.

As the steel sheet material for the Ni plated steel sheet for a positiveelectrode can for an alkaline manganese battery of the presentinvention, ultra-low carbon steel with Ti and Nb added alone or incombination, low carbon Al type steel, B added low carbon steel, or thelike, may be preferably used.

The Ni plated steel sheet for a positive electrode can for an alkalinemanganese battery according to an exemplary embodiment of the presentinvention can be manufactured by degreasing and acid pickling of steelsheets followed by Ni plating applied to the steel sheets in a Niplating bath with current density adjusted to obtain a plating layer ofdesired thickness, and by subjecting the steel sheet after platingprocess to heat treatment in an oxygen-free atmosphere at about 800° C.For Ni plating, it may be desirable to use a plating bath of low platingefficiency or to use high current density, within the range that doesnot give rise to a burnt deposit, in order to introduce strain into theplating layer. Preferably, temper rolling is performed after the heattreatment, as may be preferred.

By using the above-described heat treatment, a Ni diffusion layer isformed between the steel sheet and the plating layer, and, e.g., at thesame time, sub-micron pinholes can be formed in the Ni plating layerand/or in the Ni diffusion layer.

Using presses such as a DI press or a transfer press, a positiveelectrode can for an alkaline manganese battery of the present inventioncan be obtained from the Ni plated steel sheet thus obtained by ashaping and forming process.

EXAMPLES

Samples in the Examples were fabricated starting from an unannealedNb—Ti—Sul. C (Ti and Nb containing super low carbon) steel sheet of 0.3mm in sheet thickness as a sheet material, and after degreasing and acidpickling, Ni based plating was applied under varied plating condition in2 passes of down-pass and up-pass in a vertical plating cell, followedby heat treatment in an oxygen free atmosphere under varied heattreatment conditions, and then by temper rolling, to obtain samples usedin the Examples.

Plating conditions such as type of plating bath, current density, platedamount of Ni plating, etc., and conditions for the heat treatment afterplating are as shown in Table 1. For comparison, samples for comparativeExamples were fabricated in a method similar that in the Examples.Plating conditions such as type of plating bath, current density, platedamount, etc., and conditions for the heat treatment after plating are asshown in Table 1. Each of the samples was evaluated in observation ofsurface condition, evaluation of the battery performance, evaluation ofcorrosion resistance of the can internal surface, and evaluationcorrosion resistance of the can external surface, using methods asdescribed below.

TABLE 1 Conditions for Ni plating and for heat treatment Ni platingcondition Ni plated Steel sheet Current amount (g/m²) Classifi-Thickness density Internal External Heat treatment cation No. Material(mm) Plating bath (A/dm²) surface surface condition Example 1 Nb—Ti— 0.3Dull 75 12 12 800° C. × 20 sec 2 Sul.C Watt bath⁽¹⁾ 4 27 790° C. × 40sec 3 Boric acid 10 18 27 800° C. × 20 sec free bath⁽²⁾ Comparative 1Nb—Ti— 0.3 Dull 10 18 18 780° C. × 20 sec example Sul.C Watt bath ⁽¹⁾

-   (1) Dull Watt bath: Ni sulfate: 340 g/l: Ni chloride: 70 g/l: boric    acid: 45 g/l-   (2) Boric acid free bath: Ni sulfate: 200 g/l: sulfuric acid: 10 g/l    (Observation of Surface Condition)

The surface corresponding to the can internal surface was observed usingSEM (accelerating voltage 15 KV, magnification ×5000). Number ofpinholes of 0.1˜1 μm in diameter was counted, and was reported as numberper 10 μm×10 μm.

(Method for Evaluating Battery Performance)

A positive electrode can formed from the above-mentioned steel sheetsamples by press working was used to fabricate an ordinary LR6 typealkaline manganese battery, and the fabricated battery was stored for 40days at 60° C. and 70% RH. Internal resistance was measured with an ACresistance meter. An internal resistance of 120 mΩ or less was evaluatedas , 121˜150 mΩ as ◯. 151˜200 mΩas Δ, and 201 mΩ˜as ×.

(Method for evaluating corrosion resistance of the can internal surface)

A positive electrode can formed from the above-mentioned steel sheetsamples by press working was degreased, and after the end surface wassealed with wax, was allowed to be left in an atmosphere at 60° C. and90% RH for 3 days. Thereafter, the internal surface was inspectedcarefully using a loupe (×10) to check for the occurrence of rust. Norust was evaluated as “◯”, and occurrence of rust was evaluated as “x”.

(Method for Evaluating Corrosion Resistance of the Can External Surface)

Corrosion resistance: A positive electrode can formed from theabove-mentioned steel sheet samples by press working was degreased, andafter the end surface was sealed with wax, was placed in a salt spraytester (in accordance with JIS-Z-2371) with the external surface of thepositive electrode terminal facing upwards. After testing for 3 hours,the positive electrode can was removed from the tester, and after beingwashed with water and dried, was inspected for the presence or absenceof red rust. No rust was evaluated as “◯”, and occurrence of rust wasevaluated as “×”.

The result is shown in Table 2. As is evident from Table 2, goodcharacteristics were obtained with the Examples of the presentinvention.

TABLE 2 Result of performance evaluation Condition of surface to be usedas can internal surface Number of Corrosion Corrosion Submicronresistance resistance Condition pinholes Battery of internal of externalof surface (pcs/10 μm × 10 μm) performance surface surface Example 1 AsFIG. 2 120 ◯ ◯ 2 As FIG. 2 170 ◯ ◯ 3 As FIG. 2 60 ◯ ◯ Comparativeexample 1 As FIG. 3 10 X ◯ ◯

INDUSTRIAL APPLICABILILY

The exemplary embodiments of the present invention provides a platedsteel sheet used for a positive electrode can for an alkaline manganesebattery and a positive electrode can for an alkaline manganese batterywherein, by forming a Ni-based diffusion plating layer on the surface tobe used as an internal surface of the can, such that many sub-micronpinholes are formed on the surface, good battery characteristics can beobtained and, while eliminating the problems associated with the priorart battery, an increase in contact resistance can be prevented evenafter being stored at high temperature for a long period.

1. A Ni plated steel sheet arrangement adapted to be used for a positiveelectrode can for an alkaline manganese battery, comprising: at leastone steel sheet portion having a surface to be used as an internalsurface of the can; and a Ni based diffusion plating layer havingpinholes and provided on the surface of the steel sheet portion, thepinholes being observed by a Scanning Electron Microscope to have adiameter in the range of approximately 0.1 μm to 1 μm, and to have adensity of at least 30 pcs/(10 μm×10 μm) on the surface of the steelsheet portion.
 2. The steel sheet arrangement according to claim 1,further comprising a Fe—Ni diffusion plating layer provided on thesurface of the steel sheet portion, wherein the Fe—Ni diffusion platinglayer and the Ni based diffusion plating layer are adapted to be used asan external surface of the can.
 3. The steel sheet arrangement accordingto claim 2, wherein the Ni based diffusion plating layer is softened byrecrystallization.
 4. A positive electrode can arrangement for analkaline manganese battery, comprising: a steel sheet including asurface adapted to be used as an internal surface of the canarrangement; and a Ni based diffusion plating layer having pinholes onits surface and provided on the surface of the steel sheet, the pinholesbeing observed by a Scanning Electron Microscope to have a diameter inthe range of approximately 0.1 μm to 1 μm, and to have a density of atleast 30 pcs/(10 μm×10 μm) on the surface of the steel sheet.
 5. The canarrangement according to claim 4, further comprising a Fe—Ni diffusionplating layer provided on the surface of the steel sheet, wherein theFe—Ni diffusion plating layer and the Ni based diffusion plating layerare adapted to be used as an external surface of the can arrangement. 6.The can arrangement according to claim 4, wherein the Ni based diffusionplating layer is softened by recrystallization.